g ++ STL容器initializer_list行为之间的差异在4.4和4.7之间 [英] Differences in g++ STL container initializer_list behavior betweeen 4.4 and 4.7

问题描述

以下c ++ 0x / c ++ 11功能（初始化列表，包括对于STL容器）应该允许我在声明时初始化此STL std :: map 。并且，它的工作原理很好在g ++ 4.7.2，但我得到一个错误尝试编译它在g ++ 4.4.6。根据GCC文档，这个c ++ 0x功能在4.4中可用，但是显然（a）我做错了，或者（b）它在g ++ 4.4中不完整。

  std :: map< std :: string，std :: vector< std :: string> 
 DbConnection :: attrs_of_type = {
 {http，{url，ipaddress，port，
username，password}}，
 {email，{address，full_name}}，
 {ftp，{hostname，ipaddress，port，
username filename}} 
};但是，当我尝试编译是在gcc 4.4.6下，我得到以下<$ c   $ c>无匹配函数调用错误，通常是几乎不可能理解的方式：
  database.cc:164：error：没有匹配函数调用'std :: map< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > >，std :: less< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > >，std :: allocator< std :: pair< const std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > > > > > :: map（<括号括起始化程序列表>）'
 /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include /c++/4.4.6/bits/stl_map.h:195：注意：候选是：std :: map< _Key，_Tp，_Compare，_Alloc> :: map（std :: initializer_list< std :: pair< const _Key， _Tp>>，const _Compare& const _Alloc&）[with _Key = std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，_Tp = std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > >，_Compare = std :: less< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > >，_Alloc = std :: allocator< std :: pair< const std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > > > >] 
 /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h： 181：注意：std :: map< _Key，_Tp，_Compare，_Alloc> :: map（std :: map< _Key，_Tp，_Compare，_Alloc>&&&）[with _Key = std :: basic_string& std :: char_traits< char>，std :: allocator< char> >，_Tp = std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > >，_Compare = std :: less< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > >，_Alloc = std :: allocator< std :: pair< const std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > > > >] 
 /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h： 170：note：std :: map< _Key，_Tp，_Compare，_Alloc> :: map（const std :: map< _Key，_Tp，_Compare，_Alloc>&）[with _Key = std :: basic_string& :: char_traits< char>，std :: allocator< char> >，_Tp = std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > >，_Compare = std :: less< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > >，_Alloc = std :: allocator< std :: pair< const std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > > > >] 
 /usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h： 150：note：std :: map< _Key，_Tp，_Compare，_Alloc> :: map（）[with _Key = std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，_Tp = std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > >，_Compare = std :: less< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > >，_Alloc = std :: allocator< std :: pair< const std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: vector< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> >，std :: allocator< std :: basic_string< char，std :: char_traits< char>，std :: allocator< char> > > > > >] 
  
（是否可以更改粘贴格式，多少水平滚动？）
 
 
 
无论如何。在这一点上，我试图找出我要做不同的，以使这个初始化在g ++ 4.4.6工作。对于我声明 std :: map 或 std :: vector 的方式，这会解决问题吗？或者必须使用完全不同的方法，因为在g ++ 4.4中对这个c ++ 11特性的不同和/或不完全的实现？
解决方案
您的代码正确无误。 g ++  -  4.4官方支持初始化列表。但我记得（我遵循wg21文件），有一个关注，特别是无法初始化容器在某种程度上你在做的事情（嵌套）在某种程度上。
 
 
 
很可能，由于这些更改之后做的更改，g ++  -  4.4没有完全支持 std :: initializer_list 语法。
 
The following c++0x/c++11 feature (initializer lists, including for STL containers) should allow me to initialize this STL std::map at declaration.  And, it works just fine in g++ 4.7.2, but I get an error trying to compile it in g++ 4.4.6.  According to the GCC docs, this c++0x feature was available in 4.4, but clearly either (a) I'm doing something wrong, or (b) it was incomplete in g++ 4.4.
std::map<std::string,std::vector<std::string>>
DbConnection::attrs_of_type = {
    { "http",           { "url", "ipaddress", "port",
                            "username", "password" } },
    { "email",          { "address", "full_name" } },
    { "ftp",            { "hostname", "ipaddress", "port",
                            "username", "password", "filename" } }
};
But, when I try to compile is under gcc 4.4.6, I get the following no matching function call error, in it's typical "nearly impossible to comprehend" way:
database.cc:164: error: no matching function for call to ‘std::map<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > > >::map(<brace-enclosed initializer list>)’
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h:195: note: candidates are: std::map<_Key, _Tp, _Compare, _Alloc>::map(std::initializer_list<std::pair<const _Key, _Tp> >, const _Compare&, const _Alloc&) [with _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, _Compare = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h:181: note:                 std::map<_Key, _Tp, _Compare, _Alloc>::map(std::map<_Key, _Tp, _Compare, _Alloc>&&) [with _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, _Compare = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h:170: note:                 std::map<_Key, _Tp, _Compare, _Alloc>::map(const std::map<_Key, _Tp, _Compare, _Alloc>&) [with _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, _Compare = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_map.h:150: note:                 std::map<_Key, _Tp, _Compare, _Alloc>::map() [with _Key = std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _Tp = std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > >, _Compare = std::less<std::basic_string<char, std::char_traits<char>, std::allocator<char> > >, _Alloc = std::allocator<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::vector<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > >]
(is it possible to change how that paste is formatted, so it doesn't require as much horizontal scrolling?)

Anyway.  At this point I'm trying to figure out what I have to do differently to get this initialization to work in g++ 4.4.6.  Is there something I can change about the way I declare the std::map, or the std::vector, that will solve the problem?  Or must a wholly different approach be used due to a different and/or incomplete implementation of this c++11 feature in g++ 4.4 ?
解决方案
Your code is correct. g++-4.4 officially supports initializer lists. But I recall (I follow wg21 papers) that there was a concern, specifically about not being able to initialize containers in the way you are doing (with nesting) in the commitee at some point.

It's likely that g++-4.4 has no complete support for std::initializer_list syntax due to these changes that were done later in time.

                        
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